From data representation to data model : meta-semantic issues in the evolution of SGML

By shifting documents from display-centered media to database data SGML has raised new problems that the standard itself was not intended to solve. A database is an open world with many potential products, and most importantly, with the possibility of change. Database systems that manage change have several responsibilities. They must specify the operations that cause change and their logical properties, they must support the denition of constraints that identify valid changes, they must provide techniques for handling concurrent changes, and they must preserve the continuity of the data's essence while it changes. Handling these responsibilities constitutes the semantics of a database system. We discuss some issues that are 'meta-semantic': issues that lie behind every semantics, but that are peculiar to none. We discuss three issues - equivalence, redundancy, and operations - that are implicit in current systems and approaches. By making these issues explicit, we hope to provide the beginnings of a framework for comparison of the semantics of existing systems, and the development of more advanced ones.